1. Field of the Invention
The present invention relates to a technique for preprocessing of a weight function, etc. attaching a predetermined characteristic to a waveform signal in time domain, and primarily to a signal processing technique intended to suppress and reduce spurious components and a side lobe of a transmission signal generating apparatus, a signal processing apparatus and an antenna unit.
2. Description of the Related Art
In a conventional radar device, as described in, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 11-194166 and 2002-181921, the coefficient of a weight function is produced in time domain and multiplied by a reception signal in order to reduce the side lobe level in signal processing, pulse compression and aperture plane distribution of an antenna.
This processing in time domain, however, cannot suppress the side lobe in frequency domain, and the signal processing loss poses a great problem. Under the circumstances, however, the aperture plane distribution of the antenna is generally accompanied by a large loss, and the side lobe level is not sufficiently reduced. Further, the spurious frequency component of the transmission signal often cannot be suppressed sufficiently. Furthermore, in the correlation processing in the pulse compression, etc., the unnecessary wave components (range side lobe) generated in the signal processing often mask a minute input signal.
As a result, in a communication apparatus typically represented by the conventional radar device, an attempt to improve the characteristics is made by multiplication of the weight function on a time axis. Nevertheless, the signal processing loss is still so large that an improvement is desired.